Combined effect of precipitation and earthquakes on the kinematic

of a slow moving landslideThe case of the Maca landslide, Colca Valley, Peru

Bontemps NoélieLarose EricLacroix Pascal

Taipe EduJara Jorge

Why studying slow moving landslides ?

• displacement of the ground due to the gravity

• One of the major threat in mountainous area

• Kinematic driven by different forcings

rapid landslides (m/s)

slow moving landslides (m/an)

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Zerathe et al. , 2016

Lacroix et al. , 2014

Days since the earthquake

Cu

mu

lati

ve d

isp

lace

men

t(c

m)

Me

anve

loci

ty(c

m)

Dai

ly r

ain

fall

(mm

)

10

20

30

10

30

50

Jan 12 Jan 13 Jan 14

Jan 12 Jan 13 Jan 14

Date

Date

Landslide forcing

0

2

4

6

-2

-40 0 40 80 120

earthquake

Human activitiesRiver

rainfall

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problematic

• To better understand the different mechanisms impacting landslide kinematics in active seismic region where both earthquake and rainfall can combine

Use of in-situ data

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Site of study

Bontemps et al. 2018

• Colca river contributing to erosion of lacustrine deposits

• Precipitation follows a season cycle

• intense seismic activity

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The Maca Landslide monitoring

Zerathe et al., 2016

Recording continuously since the beginning of 2016

MAC 3

MAC 2

MAC 1

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6

Weaver (Phys. Rev. Lett. 2001; Science 2005)

𝑉𝑠 =𝜇

𝜌

In rigidity (𝜇)Increase in density (𝜌)

Vs

Method Ambient noise correlation

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=> Monitoring of tiny changes in the soil properties

Earthquake recorded between 2016 and 2017

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Effective precipitation recorded between 2016 and 2017

GPS measurements

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• Combined effect of precipitation and earthquake observable with GPS

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• Co-seismic drop of the seismic surface wave velocity => decrease of the rigidity

• Long term effect of precipitation following a strong shaking event

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Small magnitude earthquake impact (Ml<4)Distance source –landslide :

Ml 3.9 => 7kmMl 3.6 => 3.5 km

• Keefer (1984) and Keefer and Wilson (1989).

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Small magnitude earthquake impact (Ml<4)

Conclusions

• We can see a combination of earthquake and precipitation from GPS time-series

• acceleration of the landslide following low magnitude earthquakes (Ml<4)

• One possible mechanism at the origin is the damage of the soil that ease the way of precipitation into the ground

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Thank you for your attention

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